Abstract
The human foot is considered to be morphologically adapted for habitual bipedal locomotion. However, how the mobility and mechanical interaction of the human foot with the ground under a weight-bearing condition differ from those of African great apes is not well understood. We compared three-dimensional (3D) bone kinematics of cadaver feet under axial loading of humans and African great apes using a biplanar X-ray fluoroscopy system. The calcaneus was everted and the talus and tibia were internally rotated in the human foot, but such coupling motion was much smaller in the feet of African great apes, possibly due to the difference in morphology of the foot bones and articular surfaces. This study also found that the changes in the length of the longitudinal arch were larger in the human foot than in the feet of chimpanzees and gorillas, indicating that the human foot is more deformable, possibly to allow storage and release of the elastic energy during locomotion. The coupling motion of the calcaneus and the tibia, and the larger capacity to be flattened due to axial loading observed in the human foot are possibly morphological adaptations for habitual bipedal locomotion that has evolved in the human lineage.
Highlights
The anatomy of the human foot complex is quite different from that of the biologically closest living species, African great apes, owing to morphological adaptations for obligate bipedal walking that have evolved in the human lineage [1,2,3,4]
Using a biplane X-ray fluoroscopy system, we characterized the innate mobility of the human foot determined by its morphology and structure, and we found that axial loading of the human foot resulted in eversion of the calcaneus and internal rotation of the talus and tibia due to the innate morphology of the human foot [18]
The lateral plantar process (LPP) is positioned plantarly [9], making the calcaneus tend to rotate in the everting direction when the foot is axially loaded
Summary
The anatomy of the human foot complex is quite different from that of the biologically closest living species, African great apes, owing to morphological adaptations for obligate bipedal walking that have evolved in the human lineage [1,2,3,4]. Loss of opposable halluces [1,5], the presence of a longitudinal arch [6,7], formation of a large, robust calcaneus [8,9], increased rigidity of the midfoot [10,11,12] and shortening of the phalanges [13] are some of the morphological features that distinguish the human foot from that of the African great apes that are considered adaptive for generation of efficient and stable bipedal locomotion. How the specialized morphological features of the human foot facilitate generation of stable and energetically efficient bipedal locomotion has not been fully elucidated due to the complexity of the foot skeletal system, as well as the difficulty associated with the measurement of the foot bones during locomotion, which are invisible due to soft tissues surrounding the foot bones
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